Hydraulic accumulator

ABSTRACT

Disclosed is a hydraulic accumulator, particularly a piston-type accumulator, comprising an accumulator housing ( 1 ) which defines a longitudinal axis ( 9 ) and is provided with an opening that is concentric with the longitudinal axis ( 9 ) and is closed by means of a lid ( 11 ). Said lid is secured in a form-fitting manner against axial forces by means of a wall portion ( 25 ) of the accumulator housing ( 1 ), which encompasses the lid and is radially deformed towards the inside. The inventive hydraulic accumulator also comprises at least one part ( 39 ) that is deformed perpendicular to the longitudinal axis ( 9 ) so as to secure the lid ( 11 ) in a form-fitting manner against being twisted relative to the longitudinal axis ( 9 ).

The invention relates to a hydraulic accumulator, a piston-type accumulator in particular, having an accumulator housing defining a longitudinal axis, a housing having on at least one end an opening in the housing concentric with the longitudinal axis and closed by a cover which is positively locked against the action of axial forces by a wall element of the accumulator housing surrounding the cover of the housing and is deformed radially inward.

Hydraulic accumulators of this kind are available commercially and are widely used in conjunction with hydraulic systems. A hydraulic accumulator of this type, for example, is marketed by Parker Hydraulics under the trade name ACP Series Accumulator.

Hydraulic accumulators of this kind are characterized by comparatively low production costs, since the cover closing the accumulator housing through formation of positively locking engagement of cover and the part of the accumulator housing surrounding it may be fastened by simple and efficient means, in that the wall surrounding the cover, in the case of the piston-type accumulator the respective cylindrical tube, is deformed by rolling so that an annular ring projecting inward is formed and is engaged in an associated annular groove in the circumference of the cover.

The type of fastening of one or both housing cover(s) of conventional hydraulic accumulators, which is advantageous from the viewpoint of simple and cost-effective manufacture, nevertheless creates problems with respect to the operating properties and leads to difficulties in installation of such accumulators. While the positive locking of the cover and the wall element of the accumulator housing surrounding it effected by deformation rolling does ensure axial retention of the cover involved, this cover may nevertheless be twisted when torque of a certain strength relative to the longitudinal axis occurs. This results in problems, for example, when torque is applied to the respective cover as a result of the forces of tightening screw connections in installation of such accumulators in a hydraulic system by means of screw connections joining the cover on the fluid side, for example, to the outlet of a hydraulic pump. Forces such as vibrations which occur during operation may also cause torsion of the cover relative to the accumulator housing.

On the basis of this state of the art the object of the invention is to develop a hydraulic accumulator which may be simply and cost-effectively produced but is distinguished by improved connection of accumulator housing to housing cover.

It is claimed for the invention that this object is attained in the case of a hydraulic accumulator of the type described in the foregoing in that there is provided at least one part of the opening in the housing and/or the cover which is deformed transversely relative to the longitudinal axis as a positive locking feature preventing torsion of the cover relative to the longitudinal axis.

The operating or installation problems indicated in the foregoing are eliminated in that the respective housing cover is, as claimed for the invention, not only secured axially but also is secured on the accumulator housing and/or cover against torsion by additional deformation transversely to the longitudinal axis which protects the cover against torque which is active between the cover and the accumulator housing. The additional deformation required for protecting the cover against torsion may be performed without difficulty during manufacture, for example, by means of an additional pressure application or molding cycle, so that no significant increase in production costs is to be expected.

The protection against torsion may, for example, have a flattened area which is made in the circumferential annular surface of the respective cover and is pressed into a wall element of the opening in the accumulator housing, for example, an end section of the cylindrical tube in the case of a piston-type accumulator.

The configuration may be such that several flattened areas are provided around the circumference of the cover involved. These flattened areas may be arranged so that they effect transition one into the other to form a polygonal shape.

Another optional configuration of the protection against torsion is such that there is provided on the circumference of the cover a serration which may be pressed into the wall of the opening in the accumulator housing, the wall of the cylindrical tube in the case of a piston-type accumulator.

In another embodiment a groove is made in the circumference of the respective cover to effect protection against torsion. This groove is threaded over the circumference relative to the longitudinal axis and a wall element of the opening in the accumulator housing projecting as a protuberance radially inward, the cylindrical tube, for example, may be pressed into this groove. An embodiment such as this is characterized by the possibility of especially simple and cost-effective production, since, as is explained in greater detail in what follows, in addition to the rolling process for axial fastening only one additional rolling or chasing tool need be employed over the circumference of the accumulator housing surrounding the cover. If the tool runs over the spiral groove which extends over an axial area of the cover on the basis of the thread pitch, a wall element extending inward as a protuberance is pressed into the spiral groove.

The invention is explained in detail in what follows with reference to exemplary embodiments illustrated in the drawing, in which

FIG. 1 shows a greatly simplified diagram of a longitudinal section of a hydraulic accumulator of the state of the art configured as a piston-type accumulator;

FIG. 2 a greatly simplified diagram of a front view of the end on the fluid side of an exemplary embodiment of the hydraulic accumulator claimed for the invention in the form of a piston-type accumulator;

FIG. 3 a section along line III-III corresponding exclusively to the end area of the exemplary embodiment shown in FIG. 2;

FIG. 4 a side view, on a scale larger than that of FIGS. 1 to 3, of a housing cover of another exemplary embodiment of the hydraulic accumulator claimed for the invention; and

FIG. 5 a sectional view, on a scale smaller than that of FIG. 4, exclusively of the end area on the fluid side of the exemplary embodiment incorporating the built-in cover of FIG. 4.

For the sake of simplification of illustration the relevant sealing elements employed for sealing between housing cover and accumulator housing are omitted from the drawings, in which FIG. 1 shows a piston-type accumulator of conventional design, FIGS. 2 and 3 a first exemplary embodiment of the hydraulic accumulator claimed for the invention, and FIGS. 4 and 5 illustrate a second exemplary embodiment of the hydraulic accumulator claimed for the invention.

All the embodiments illustrated represent piston-type accumulators, in which a cylindrical tube 1 is provided as accumulator housing. In the exemplary embodiments shown the material provided for the cylindrical tube 1 is steel of a ductility suitable for deformation by pressing or rolling. The cylindrical tube 1 contains a piston 3, shown only in FIG. 1, as the element separating the fluid side 5 from the gas side 7 of the accumulator. The opening, concentric with the longitudinal axis 9, in the cylindrical tube 1, is closed at the end on the fluid side 5 by a round housing cover 11. On the gas side 7 the opening, concentric with the longitudinal axis 9, in the cylindrical tube 1 is closed on the end by a housing cover 13. The latter has a central boring 15 for a gas valve. The cover 11 on the fluid side 5 also has a central boring 17 for connection to a hydraulic system.

Each cover 11, 13 has in its end area facing the piston 3 an annular groove 19 made in its circumference as seat for a sealing element not shown in the figures, an O-ring, for example. Another annular groove 21 is made in the circumference of the cover, axially offset from the annular groove 19 in the direction of the other end of the cover. This annular groove 21 serves the purpose of axial fastening of the cover 11, 13 in the cylindrical tube 1, while positive engagement of cylindrical tube 1 and annular groove 21 is established by a process of pressing in or rolling in which an outer groove 23 is formed on the circumference of the cylindrical tube 1 as a result of which an annular bead 25 is formed which is engaged in the annular groove 21.

In the exemplary embodiment illustrated in FIGS. 2 and 3 the cover 11 has in its outer end area a flattened section 27, specifically on its axially outer end edge 29. The end section 31 of the cylindrical tube 1 oriented toward the flattened section 27 is pressed into this section. The cover 11 secured axially by engagement of the annular bead 25 in the annular groove 21 is thus additionally secured at the flattened section 27 against torsion about the longitudinal axis 9.

In the exemplary embodiment illustrated in FIGS. 4 and 5 the cover 11 has, between the annular groove 21 and the axially outer end edge 29, another annular groove 35 which extends in the form of a spiral, that is, a thread pitch, relative to the longitudinal axis 9. As is to be seen in FIG. 5, another groove 37 by which the wall material of the cylindrical tube 1 is pressed as a protuberance 39 into the spiral annular groove 35 is formed by a pressing or rolling process which is carried out on the cylindrical tube 1 in the axial section over which the spiral annular groove 35 extends. A protuberance 39 is formed in that an indentation is made not over the entire circumference of the cylindrical tube 1 but exclusively in the area in which the pressing or rolling tool passes over the spiral annular groove 35. As a result, the protuberance 39 produced only at this point forms a discontinuity which acts as a lock on the protuberance to prevent torsion caused by the sloping surfaces adjacent to the thread pitch of the annular groove 35 on the protuberance 39. The part of the spiral annular groove 35 not containing the protuberance 39 remains clear, as is to be seen at 41, where the end of the annular groove 35 adjoining the end edge 29 is to be seen.

Cogging, such as that in the form of knurling, may be provided on the respective cover in place of the two configurations of the protection against torsion illustrated in the drawing. Several flattened sections may also be provided on the circumference of the respective cover, it being possible to provide any shapes desired which result in a configuration other than a round one on the respective cover, such as one in the form of a polygon. 

1. A hydraulic accumulator, a piston-type accumulator in particular, having an accumulator housing (1) defining a longitudinal axis (9), such accumulator housing (1) having on at least one end an opening in the housing concentric with the longitudinal axis (9), such opening in the housing being closed by a cover (11, 13) which is positively secured against axial forces by a wall element (25) of the accumulator housing (1) deformed radially inward surrounding such cover (11, 13), characterized in that at least one part (27, 39) of the opening in the housing and/or the cover (11) deformed transversely to the longitudinal axis (9) is provided as positive locking against torsion of the cover (11) relative to the longitudinal axis (9).
 2. The hydraulic accumulator as claimed in claim 1 in the form of a piston-type accumulator having a cylindrical tube (1) serving as accumulator housing in which a piston (3) separating the gas side (7) from the fluid side (5) is movable and which is closed by a cover (11, 13) on both sides of which at least the cover (11) present on the liquid side (5) is secured against torsion.
 3. The hydraulic accumulator as claimed in claim 1, wherein the protection against torsion has at least one flattened section (27) which is worked into the circumferential annular surface of the cover (11) and into which a wall section (31) of the opening of the accumulator housing (1) is pressed (FIG. 2).
 4. The hydraulic accumulator as claimed in claim 3, wherein the flattened section (27) is provided in the area of the axially external end edge (29) of the cover (11) and wherein the end edge of the opening in the accumulator housing (1) is pressed into the flattened section (27).
 5. The hydraulic accumulator as claimed in claim 4, wherein a plurality of flattened sections (27) is provided, which flattened sections are distributed over the circumference of the cover (11).
 6. The hydraulic accumulator as claimed in claim 5, wherein the flattened sections (27) are configured so as to undergo transition one into the other for the purpose of forming a polygonal shape.
 7. The hydraulic accumulator as claimed in claim 1, wherein, for the purpose of forming protection against torsion, there is provided on the circumference of the cover (11) a serration against which the wall of the opening in the accumulator housing (1) may be pressed.
 8. The hydraulic accumulator as claimed in claim 1, wherein, for the purpose of forming protection against torsion, there is worked into the circumference of the cover (11) a groove (35) which extends in a thread pitch along the circumference and into which a wall section (39) of the opening in the accumulator housing (1) projecting radially inward as a protuberance may be pressed.
 9. The hydraulic accumulator as claimed in claim 1, wherein the cover (11, 13) has, in the vicinity of the edge facing the interior of the accumulator housing (1), a circumferential annular groove (19) as seat for a sealing element and wherein there is worked into the cover (11, 13), between this annular groove (19) and the protection of the cover (11, 13) against torsion a second annular groove (21) into which the wall section (25) of the accumulator housing (1) surrounding the cover (11, 13) as protection from axial forces is pressed. 